Bridging the gap between biomass and petrochemicals

A few papers describe methods of using biomass feedstocks to create …

This week's issue of Science takes a look at work that could help bridge the gap between biomass fuel production and traditional petrochemical engineering. Modern society relies on petrochemicals not only for our primary transportation needs, but also for most of the chemicals and polymers that we use. With the increased focus on using woody and agricultural stock to create biofuels, most notably bioethanol, it is worth asking if these feedstocks can support the rest of our petrochemical needs.

The issue contains a letter that focuses on two papers published this year, one by Bond et al. in Science, and one by Lange et al. in Angewandte Chemie International Edition. The articles look into whether carbohydrates from biorefining processes can be used to create compounds that look and react like more traditional petrochemical feedstocks, which have less oxygen than carbohydrates. If this is possible—or, more importantly, if it is feasible—then biomass could be used as a starting material for our existing petrochemical infrastructure.

The two papers focus on the compound levulinic acid, which is formed, along with formic acid, when six-carbon sugars are reacted with acids. The levulinic acid can undergo a hydrogenation reaction to form γ-valeroactone (GVL), at which point the two papers diverged.

Bond's team proposed a method that would eliminate CO2 from the GVL in water, giving a mixture of isomeric butenes; these can be linked together, or oligimerized, into longer hydrocarbons and be used directly as fuels. As an added bonus, this process is carried out at a pressure where the CO2 could be reused in other reactions or ready made for sequestration without the need for an expensive compression step.

Lange's team, on the other hand, reacted GVL to form valeric acid (VA) with fairly high completion and selectivity. The VA could then be combined with various alcohols to form Valerate esters. Low molecular weight esters (up to propyl) were found to be suitable gasoline additives, working at 10 to 20 percent by volume. Higher weight esters could act either as a diesel additive or as diesel fuel itself.

The letter acknowledges that there are "technology development" hurdles that must be overcome before either of these processes go into production, let alone steal the spotlight from bioethanol. Even in the face of the challenges, the letter argues that these are promising demonstrations that biofuel stocks can produce intermediates that can be directly inserted into our existing petrochemical plants and processes. The perspective concludes with the hope that such research will spur the use of renewables as a replacement for our limited supply of petrochemical raw materials.

Matt Ford / Matt is a contributing writer at Ars Technica, focusing on physics, astronomy, chemistry, mathematics, and engineering. When he's not writing, he works on realtime models of large-scale engineering systems.